This invention relates to hydrophilically end-capped polyurethane thickeners having particular utility in paints, coatings and other aqueous systems.
Thickeners have been known for use in paints and coatings for many years. They can be naturally occurring or synthetically manufactured. Examples of naturally occurring thickeners include alginates, casein, gum karaya, locust bean gum, cellulosics such as methyl cellulose, hydroxyethyl cellulose and hydroxypropylmethyl cellulose.
Examples of synthetic thickeners include the compositions of U.S. Pat. Nos. 4,079,028 (Emmons et al.), 4,180,491 (Kim et al.), 4,327,008 (Schimmel et al.), 4,373,083 (Seiner et al.), 4,426,485 (Hoy et al.), 4,436,862 (Tetenbaum et al.), 4,496,708 (Dehm et al.) and 4,514,552 (Shay et al.).
U.S. Pat. No. 4,079,028 purports to teach latex systems containing a low molecular weight polyurethane thickener characterized by at least three hydrophobic groups interconnected by hydrophilic polyether groups.
U.S. Pat. No. 4,180,491 purports to teach nonionic polyurethane thickeners for print pastes, which thickeners are characterized by a molecular weight of at least 10,000 and having at least three hydrophobic branching groups linked through hydrophilic polyether segments.
U.S. Pat. No. 4,327,008 purports to teach rheology modifiers useful in water-based and organic solvent-based compositions, which modifiers are derived from the reaction of polyalkylene oxide, polyfunctional material (such as polyol, amine, amine alcohol, thiol or polyisocyanate), diisocyanate, water and a monofunctional active hydrogen-containing compound or monoisocyanate.
U.S. Pat. No. 4,373,083 purports to teach a process for making rheology modifiers (particularly those of U.S. Pat. No. 4,079,028) useful in water and organic solvent-based compositions, which modifiers are derived from the reaction of polyalkylene oxide, polyfunctional material (such as polyol, amine, amine alcohol, thiol or polyisocyanate), diisocyanate, water and end-capping compounds in an organic solvent.
U.S. Pat. No. 4,426,485 purports to teach water soluble, thickeners for aqueous systems which are characterized by deliberate, arranged bunches of hydrophobes bonded to a water-soluble backbone.
U.S. Pat. No. 4,436,862 purports to teach thickeners composed of a clay stabilizer and a water-dispersable polyurethane.
U.S. Pat. No. 4,496,708 purports to teach water-soluble comb polyurethane thickeners having hydrophilic polyether backbones and pendant monovalent hydrophobic groups.
U.S. Pat. No. 4,514,552 purports to teach alkali soluble thickeners which are aqueous emulsion copolymers of a,b-monoethylenically unsaturated carboxylic acid, monoethylenically unsaturated monomer (such as ethyl acrylate), nonionic urethane monomer which is the reaction product of a monohydric surfactant and a monoisocyanate, and optionally a polyethylenically unsaturated monomer.
In contrast to the above, the present invention relates to hydrophilically end-capped polyurethane thickener compositions which are particularly suited for use in paint and coating compositions. Whereas the patents discussed above all teach the use of hydrophobic end-capping groups to attain thickening efficiency, the present invention utilizes hydrophilic end groups.